Proper nervous system function critically depends on the proper assembly, maintenance, and activity- dependent modification of neuronal circuits. Although a great deal is known about extracellular molecules and signaling pathways that regulate axonal growth and pathfinding during embryonic nervous system development, comparatively little is known about the mechanisms that control synaptic structure and function in the juvenile and adult mammalian brain and spinal cord. Mounting evidence suggests that there is a close overlap of molecular players that limit neuronal sprouting in the injured CNS, and molecules that restrict neuronal plasticity in the healthy (uninjured) CNS. Recent studies from our lab revealed that the growth inhibitory proteins Nogo/RTN4 and oligodendrocyte myelin glycoprotein (OMgp) suppress activity-dependent synaptic plasticity in an NgR1-dependent manner. The signaling mechanisms employed by NgR1 to regulate synaptic structure and synaptic transmission have not yet been defined. This research will pursue mouse genetic, primary neuronal cell culture, and biochemistry-based approaches to define the signaling pathways regulated downstream of Nogo/NgR1, with a primary focus on the PI3K/AKT/mTORC1 pathway. In a parallel approach, a combination of electrophysiological recordings and pharmacological treatments will be used to examine the molecular mechanisms underlying the previous observations that loss of NgR1 attenuates LTD at CA3-CA1 synapses, and that application of Nogo66 decreases LTP of synaptic transmission in CA1 neurons. Behavioral studies in NgR1 germline and conditional mutants will assess the importance of NgR1 signaling in learning and memory. Because changes in neuronal structure and synaptic function often correlate with brain disease, a detailed understanding of how brain structure and function is regulated is of great interest, both biologically and clinically. Experiments proposed are a systematic analysis of Nogo receptor function, and are expected to provide insights into key aspects of nervous system physiology and pathology.